1. Field of the Invention
The present invention relates generally to a marine inboard-outboard or outboard engine. More specifically, the present invention relates to an improved water intake arrangement for an inboard-outboard or outboard engine. Still more specifically, the present invention relates to an improved water intake arrangement for inboard-outboard and outboard engines whereby the induction of cooling water into the cooling water circuit of the outboard engine can be performed efficiently regardless of the operating mode and in a manner which allows the outboard engine to be operable in a high setting mode and permit the use of a high performance super cavitation propeller, and in a shallow water mode wherein the outboard engine is partially tilted so as to permit the boat on which it is mounted, to be operated in very shallow water.
2. Description of the Prior Art
In prior art marine outboard and inboard-outboard engines it is common to employ what is referred to as a "wet" cooling system wherein, rather than recirculating a given amount of coolant through a heat exchanger system as is usually performed in automotive engines, cooling water is introduced from the body of water in which the vessel is floating, into the cooling water circuit of the outboard engine and then discharged back into the body of water, usually through the exhaust port of the outboard engine.
The induction system of the outboard engine shown in FIGS. 1-4 by way of example is disclosed in detail in JP.A.57-30691.
In FIG. 1 an exemplary outboard engine 5 having a so called "wet" type prior art cooling water induction system is depicted in a side elevational view. The outboard engine 5 is mounted on the boat, which it is intended to drive, by means of a clamp 4 which is attached to a bracket 3 formed at the upper portion of the transom 2.
The outboard engine 5 includes a torpedo 6 at the lower portion of the lower case 7, in which the gears by which the rotation imparted to the drive shaft 12 by the power unit 11 is transmitted to the propeller, are accommodated. The lower case 7 comprises a water intake 8 formed immediately above the torpedo 6 for the induction of water from the body of water in which the vessel is floating, into the cooling circuit of the outboard engine. The water drawn in through the water intake 8 is forced through the cooling circuit under pressure by means of a water pump 9. This pump is disposed within the lower portion of the upper case 10, in the immediate vicinity of the drive shaft 12 so as to be driven thereby.
The details of the torpedo 6 and the lower case 7 will be better appreciated from a consideration of FIGS. 2, 3 and 4.
As can be seen from FIG. 2, the torpedo 6 formed at the bottom of the lower case 7 accommodates pair of gears 13 by which the rotation of the drive shaft 12 imparted thereto by the power unit 11, is transmitted to the propeller shaft 14. A propeller boss 15 on which are formed propeller blades 16, is mounted on the propeller shaft 14 so as to be driven thereby.
The propeller shaft 14 extends rearwardly from the drive shaft 12 and is approximately parallel to the surface of the water. The forward end of the propeller shaft 14 is seated against a thrust bearing 50 which receives the forward thrust imparted to the propeller shaft 14 by the action of the blades 16 of the propeller as it is driven to rotate in the water.
The propeller shaft 14 in maintained in alignment within the torpedo 6 by means of the thrust bearing 50 and a bearing 18 which is formed in the vicinity of the gears 13. At the rear end of the torpedo 6, a bearing 19 is provided for further maintaining the propeller shaft 14 in alignment. An oil seal 51 is provided at the rearmost end of the casing for retaining lubricant and excluding water.
The bearings 18 and 19 are formed at opposite ends of a bearing housing 17 which is received in a cylindrical chamber 20 defined within the torpedo 6. The bearing housing 17 is sealed against the walls of the cylindrical chamber 20 at its front end and is narrowed at its central portion such as to define an empty space within the cylindrical chamber 20 of the torpedo 6. This empty space is fluidly communicated to the lower end of the outboard engine exhaust passage 21 which formed in the lower case 7 and thus defines the most downstream portion of the engine exhaust passage.
A water intake 8 is formed in the wall of the lower case 7 immediately above the torpedo 6. This water intake 8 is connected, by means of the suction passage 22, to the water pump 9 which serves to drive the water under pressure through a discharge water passage 23 and into the internal cooling circuit of the power unit 11.
However, this prior art system suffers from a number of drawbacks which prevent the operation of the same in given modes of operation as will become more clearly appreciated from the following discussion.
In FIG. 5 the outboard engine having the prior art induction arrangement, is depicted in the normal operation mode. As will be appreciated in this mode, the lower case 7 is arranged to project deeper than the bottom of the boat 1. Accordingly, even if the boat is in a condition wherein the bottom is riding on the top of the water surface 24 as occurs when the boat is planing, the water intake 8 of the outboard engine 5 is disposed well beneath the surface of the water so that an ample supply of cooling water can be easily inducted through the water intake 8.
However, it is now required to be able to operate outboard engines and the like, in modes not previously contemplated.
Among these "new" operating modes is, for example, the "shallow water" operation mode in which the outboard engine is set high in the water so as to avoid impinging on underwater obstacles thereby effectively decreasing the draft of the boat and allowing it to be operated in shallower waters.
Another of these operation modes is the "high setting" mode in which a high performance "super cavitation" propeller of the type in which only one or two of the blades is in the water at any given time is employed.
In these operating modes the outboard engine 5 is set at a level at which the upper surface of the torpedo 6 is actually at or above the water surface 24. In FIG. 6 the high set mode in which the upper surface of the torpedo 6 and the propeller boss 15 are level with the water surface is shown. In FIG. 7 the high set mode in which the upper surface of the torpedo 6 and the propeller boss 15 are actually above the water surface is shown.
FIG. 8 shows the above mentioned shallow water mode wherein the outboard engine is partially or half tilted and set for shallow water operation in a manner to avoid the bottom and/or submerged obstacles.
As can be seen, in the high setting and shallow water modes, the water intake 8 of the prior art outboard engine is located well above the water surface 24. Under these circumstances only air is inducted through the water intake 8 and the cooling system becomes "starved" of liquid coolant. This of course leads to rapid overheating and/or severe damage to the power unit 11.
What is more, even when the prior art outboard engine 5 is operated in the normal mode in which the cooling water intake 8 is disposed well below the water surface 24, there is still the possibility of cooling water induction problems.
For example, it is not uncommon in the operation of such craft that a piece of floating matter 25 such as a sheet of material such as a discarded vinyl sheet, becomes draped across the front of the lower case 7 in the manner shown in FIG. 9. In such cases the vinyl sheet 25 may cover the water intake 8 and be held firmly thereagainst by the suction produced by the water pump 9 thereby partially or completely blocking the flow of coolant water to the water pump 9 and again raising the danger that the outboard engine becomes starved of coolant and overheats.
In view of the above problems encountered in outboard engines wherein the water intake 8 is disposed on the side of the lower case 7 at a portion thereof which is located immediately above the torpedo 6, it has been proposed to form a water intake at a lower portion of the torpedo. FIG. 10 shows an example of such an arrangement.
In the FIG. 10 arrangement the 26 is located in the water intake front surface of the skeg which protrudes from the bottom of the torpedo 6. The water intake 26 is connected to the water pump 9 by a suction passage 27 which is formed at the front edge portion of the lower case. Thus, the water intake 26 is always immersed in water no matter what the operation mode of the outboard engine is.
However, this particular proposal encounters drawbacks which render it difficult to put into idea into actual practice.
These difficulties arise from the fact that, as can be appreciated from FIG. 2, a number of elements must be disposed in the limited space at the front portion of the torpedo and in its immediate vicinity. Among these are the speedometer pickup 49, the shift rod 28 and the thrust bearing 50. Thus, in practice it becomes difficult or impossible to arrange the water intake in the vicinity of the front of the torpedo because of the crowding with other essential engine elements.
One proposal for overcoming the overcrowding at the front portion of the lower case 7 is to form a cup-shaped cap on the front of the torpedo 6 in which a passage is formed for allowing the induction of cooling water.
In such a construction however, the nose cone added to the front of the torpedo poses certain disadvantages in itself in that it adds weight to the outboard engine and can have a negative effect on the overall balance of the same. Another disadvantage of such an added on nose cone is that it would protrude from the front of the torpedo 6 thus making it more likely for floating matter, such as seaweed and the like, to become caught on the front edge of the lower case 7 instead of sliding down and off of the bottom of the lower case as tends to occur in the absence of such a protrusion.
It has also been proposed in the prior art to integrally form a slightly larger nose cone at the front of the torpedo.
However, in accordance with such a design, the above problems wherein floating matter can become caught on the nose cone because it protrudes beyond the front edge of the lower case and is therefore not easily and naturally dislodged remain, while the problems that the lower case becomes generally larger and heavier, still also remain unsolved.
Examples of the above proposed nose cone water intakes are set forth in JP.A.62-283097 and JP.A.50-124394.